Polymer films are increasingly being used as substrates in fields where security, authentication, identification and anti-counterfeiting are important. Polymer-based products in such areas include for example bank notes, important documents (e.g. ID materials such as for example passports and land title, share and educational certificates), films for packaging high-value goods for anti-counterfeiting purposes, and security cards.
Polymer-based secure materials have advantages in terms of security, functionality, durability, cost-effectiveness, cleanliness, processability and environmental considerations. Perhaps the most notable amongst these is the security advantage. Paper-based bank notes, for example, can be relatively easy to copy, and there is lower occurrence of counterfeits in countries with polymer-based bank notes compared to paper-based bank notes. Polymer-based bank notes are also longer-lasting and less-easily torn.
Security materials based on polymer films are amenable to the incorporation of a variety of visible and hidden security features. Since the introduction of the first polymer bank notes approximately 25 years ago, security features have included optically variable devices (OVD), opacification features, printed security features, security threads, embossings, transparent windows and diffraction gratings. Aside from complicated security features there is also the more immediate advantage that the high temperatures used in copying machines will often cause melting or distortion of polymer base-material if counterfeiters attempt simply to copy secure materials (e.g. bank notes) using such machines.
The basic polymer substrate for such bank notes is processed using some, or all, of the following steps to arrive at the finished product:
1. Opacifying—two layers of ink (usually white) are applied to each side of the note, except for a region that is deliberately left clear, i.e. as a transparent window;
2. Sheeting—the substrate is cut into sheets suitable for the printing press;
3. Printing—one or more of traditional offset, intaglio and letterpress printing processes may be used; and
4. Overcoating—notes are coated with a protective varnish.
In-film features such as embossings, etchings, etc. are often incorporated into transparent and/or partially transparent windows in otherwise substantially opaque security documents.
As noted above, an intaglio printing process is a known method of providing printed features on such security documents. A window has become an important feature of security document substrates and is often enhanced by embossing numbers, text or images directly into the bare window. Where a security document comprises an opacified region and a window having such embossings, the embossings can be formed as part of the intaglio process. The heat and pressure of the intaglio process is such that it allows for embossing simultaneously with intaglio printing.
Current processes suffer limitations in that the embossing is often the final process and therefore cannot be integrated with opacification and/or offset printing. Further, in current processes, the embossings are effectively a free fringe benefit of the intaglio process, but security document printers charge the substrate suppliers for this feature as a separate security document feature.
Whilst the above described security documents and methods of production thereof offer features of interest, it is desirable to provide a security document and method of production thereof which offers improved properties, and thus the present invention seeks to provide for a security document and method of production thereof having advantages over known such security documents and methods of production thereof.